1. Field of the Invention
This invention relates to a procedure for determining the difference between the temperature of a heated, pressurized liquid flowing in a closed system and its saturation temperature.
2. Description of the Prior Art
Saturation is reached in such liquids under specific pressure and temperature conditions. There are many examples of applications where it is highly desirable to have precise information concerning the saturation temperature and the difference from the saturation temperature for a pressurized, heated flowing liquid. Such an application, particularly when problems occur, is the primary cooling system of a pressurized water nuclear reactor installation which has a pressure of about 2350 psi and a temperature of about 570.degree. F. When temperature instruments with a range of about 300.degree. F.-680.degree. F. and pressure instruments with a range of about 150 psi-2600 psi must be used, as in this example, it is difficult to determine pressure and temperature data precisely because of these wide ranges. That is, a typical pressure transmitter alone exhibits a measurement uncertainty on the order of plus or minus 1 lb./100 lbs. of range, so that a pressure transmitter having a range of 0- 2,500 lbs./in..sup.2 has an expected uncertainty error on the order of at least 25 lbs./in..sup.2 over its entire normal operating range. Similar measurement uncertainty is introduced by temperature measurements.
The difference between saturation temperature and actual temperature of the liquid becomes especially important, however, when that difference is relatively small, i.e., when accident conditions prevail. If saturation temperature is reached the liquid will boil, thereby reducing its ability to conduct heat from heating elements, such as fuel rods. Further, under accident conditions, the accuracy of measurements of temperature and pressure deteriorates substantially. If, for example, pressure measurement string uncertainty of 2%-3% can be achieved over a broad range under normal operating conditions, an uncertainty of 12%-15% will probably be reached under accident conditions, i.e., by increased temperature, humidity, and radiation level of the transmitter environment.
It is generally known how to establish the difference between the temperature and the saturation temperature of a liquid in the following manner. The pressure of the liquid is measured, and is converted into the pertinent saturation temperature electronically or digitally, on the basis of a precalculated or otherwise known saturation curve. The temperature of the liquid is then measured and the differential between the calculated saturation temperature and the measured actual temperature of the liquid is taken.
Because of the large ranges of the measuring devices and the combination of the pressure and temperature measurement methods with one another, the measurement errors are additive, so that no reliable statement concerning the temperature difference from the saturation temperature is possible. Under accident conditions, the much greater measurement errors further reduce meaningfulness and usefulness of the computed temperature difference from saturation.
It is therefore apparent that a substantial need exists for a method of more accurately determining the difference between the temperature of a heated pressurized liquid flowing in a closed system and its saturation temperature.